Coverage sampling is a method of increasing the quality of anti-aliasing without adding a lot of processing overhead. Instead of fully sampling a point in the pixel, coverage sampling simply detects whether or not a polygon is present and uses that information to weigh the multisamples. You can learn more about coverage sampling in our Anti-Aliasing Analysis, Part 1 article on the Coverage Sampling Modes: Nvidia’s CSAA and AMD’s EQAA page.
Nvidia's implementation is designated CSAA and AMD's is called EQAA. Since EQAA only works with the Radeon HD 6900 series, we’ll keep those results separate for now. Let’s consider the GeForce performance first:
The CSAA performance falls about where we would expect it to on the GeForce cards. The 8x CSAA and 16x CSAA modes perform in between 4x MSAA and 8x MSAA, although they often sit closer to the lighter 4x MSAA load. The 16xQ CSAA and 32x CSAA modes perform slightly slower than 8x MSAA.
Now, let’s consider EQAA on the Radeon HD 6970:
Note that the Radeon features a 2x MSAA + 2x coverage sample (2x EQAA) mode that the GeForce card doesn’t counter. On the other hand, Nvidia has 4x MSAA + 12x coverage sample (16x CSAA) and 8x MSAA + 24x coverage sample (32x CSAA) modes to which AMD can't answer. On a per-game basis, there are certainly differences in performance. However, all together, CSAA and EQAA appear to have a similar impact on the hardware.
- I'm Anti-Aliasing. As In, I Won't Stand For Aliasing.
- Test System And Benchmarks
- Multi-Sample Anti-Aliasing: 1280x1024
- Multi-Sample Anti-Aliasing: 1680x1050
- Multi-Sample Anti-Aliasing: 1920x1080
- Coverage Sample Anti-Aliasing: 1280x1024
- Coverage Sample Anti-Aliasing: 1680x1050
- Coverage Sample Anti-Aliasing: 1920x1080
- Edge-Detect Anti-Aliasing: 1280x1024
- Edge-Detect Anti-Aliasing: 1680x1050
- Edge-Detect Anti-Aliasing: 1920x1080
- Texture Transparency Anti-Aliasing: 1280x1024
- Texture Transparency Anti-Aliasing: 1680x1050
- Texture Transparency Anti-Aliasing: 1920x1080
- Morphological Anti-Aliasing: 1280x1024
- Morphological Anti-Aliasing: 1680x1050
- Morphological Anti-Aliasing: 1920x1080
- Supersampling Anti-Aliasing Benchmarks
- Multiple Anti-Aliasing Modes For Multiple Scenarios